A large and growing population of users is enjoying entertainment through the consumption of digital media items, such as music, movies, images, electronic books, and so on. The users employ various electronic devices to consume such media items. Among these electronic devices (referred to herein as user devices) are electronic book readers, cellular telephones, personal digital assistants (PDAs), portable media players, tablet computers, netbooks, laptops and the like. A basic issue with mobile devices, such as cell phones, PDAs, tables, and mobile game consoles has always been screen size. One the one hand, a large screen is beneficial for watching movies, playing games, and even reading e-mail comfortably. On the other hand, the larger the screen, the bigger the device, which may be less desirable for a light and portable product. Another problem consumers experience with portable devices, like tablet devices, is the lack of ability to immerse themselves in a tablet experience, such as watching a movie on an airplane.
One technology directed to address the size dilemma is head mounted display (HMD) systems. Conventional consumer HMD systems, such as TV glasses and virtual-reality goggles, were usually heavy, expensive and uncomfortable to use for long periods of time. More recently, lighter and more affordable products have been developed in video glasses. A HMD is a display device that is worn on the head, such glasses or goggles or that is part of a helmet. The HMD has display optics, such as lenses, which are placed in front of one or both eyes of a user. The HMD may have one display or two miniaturized displays, such as liquid crystal display (LCD), Liquid Crystal on silicon (LCos), or organic light-emitting diode (OLED).
There are some HMD systems with opaque lenses and some HMD systems with transparent lenses (also referred to as optical HMD systems or smart glasses). The opaque systems do not readily allow a user to reengage with the outside world without physically moving or removing the HMD system. On the other hand, the transparent systems do not allow a user to immerse in the experience.